There are a number of known techniques for making an electrical interconnection between a semiconductor chip and a semiconductor package. Tape-Automated Bonding (TAB) is one known technique for making such a chip-to-package interconnection. TAB uses an insulating polymer tape with a patterned metal to make a chip-to-package interconnection. The insulating tape is typically polyimide and the patterned metal is typically copper.
It is not feasible to use a TAB technique in conjunction with a sensitive packaging environment because water vapor and volatile gases are absorbed by the polymer tape during processing and handling. Thereafter, the water vapor and volatile gases can corrupt the sensitive packaging environment.
Any vacuum environment is a sensitive packaging environment. One use of a vacuum environment is in a cryogenic integrated circuit housing. As used herein, a cryogenic integrated circuit housing refers to any cooled volume that is evacuated and sealed. A cryogenic integrated circuit housing is used to reduce the operating temperature of an integrated circuit and thereby increase its operating speed.
Cryogenic integrated circuit housings endeavor to minimize all heat transfer paths. One way of accomplishing this goal is to use bond wires with very small diameters. The small diameter of the bond wire reduces thermal migration from the cooled chip environment, through the package feedthroughs, to the external pins of the package.
Unfortunately, this approach presents a major assembly problem for modern microprocessor chips that may have more than 400 external connections. It would be desirable to utilize a TAB-like approach to make connections to a cryogenically cooled semiconductor since a number of wires can be carried on a single polymer substrate. Unfortunately, as previously indicated, the polymer substrate absorbs vapor and volatile gases that are incompatible with a cyrogenically cooled package environment.
Therefore, it would be desirable to provide a high-density chip-to-package interconnection circuit that does not absorb vapor or volatile gases. Ideally, such a circuit would be formed by using processing techniques known in the art.